Slide Valve Bridle Clearance

[GWRdriver]

I'm in the process of machining the slide valves and "bridles" ( or sometimes referred to as yokes) for a locomotive, and until this project all my valves have been driven by a central stem and cross-bar in a slot.
My question is about what experiences you've had relative to clearance within a bridle drive, . . . how much is needed to allow the valve body to move vertically in the bridle without binding, yet minimize slack?  A central spindle with cross-bar has very little reason to bind, however the bridle arrangement might have a number of forces acting on it which might cause vertical binding.  Your thoughts?

FYI, the valve is bronze, the SS bridle ID is 1" x 1" and vertical width is 1/4".

[Jasonb]

I've never measured the clearance, I just do it as I would with the slot and nut by using the nut as a gauge to get a close fit but one that allows the nut to move freely without slack. It's probably in the region of 0.01mm all round. Round buckles would be reamed and that assuming your average H7 reamer and nominal size spigot on the valve would give that sort of clearance too.

You could allow a bit more sideways clearance as that won't affect the valve events

[GWRdriver]

Thanks Jason, that's exactly what I had in mind doing, including the side clearance, but it helps to have a confirmation of my thinking, and that there is probably no hidden mystery to it.